1. Field of the Invention
The present invention relates to a new and improved process for the manufacture of nitrophenetole. More particularly, the present invention relates to the manufacture of nitrophenetole by the ethoxylation of p-nitrochlorobenzene wherein the reaction is carried out in the presence of oxygen to suppress the formation of azo and azoxy compounds as by-products and wherein nitrophenetole is produced with greater conversions and greater yields.
2. Prior Art
For a variety of organic syntheses p-nitrophenetole is an important chemical intermediate. One significant commercial use of p-nitrophenetole is as an intermediate chemical in the manufacture of p-phenetidine. p-Phenetidine is an important intermediate in the manufacture of ethoxyquin, the common name of 2,2,4-trimethyl-6-ethoxy-1-H-dihydroquinoline. Ethoxyquin has found wide commercial use in reducing or suppressing the oxidation of oils in animal feeds and the like. Animal feeds having an effective antioxidant amount of ethoxyquin have significantly longer shelf life than feeds not having the same incorporated therein. p-Phenetidine is also an important intermediate compound useful in the manufacture of phenacetin, phenocoll, p-phenetyl-urea and various dyestuff intermediates.
A well-known method for the manufacture of p-nitrophenetole involves the ethoxylation of p-nitrochlorobenzene in an ethanolic solution containing an alkali metal hydroxide, such as sodium hydroxide according to the following equation: ##STR1## Unfortunately, this known reaction is plagued with the formation of azo and azoxy compounds as undesirable by-products. These by-products are the result of an exothermic side reaction of p-nitrochlorobenzene under the reaction conditions normally employed. The by-products have been identified as 4,4-dichloroazoxybenzene and 4,4'-dichloroazobenzene. When p-nitrochlorobenzene is reacted with ethanol in the presence of an aqueous solution of alkali metal hydroxide, the azo and azoxy by-products may be produced in yields as high as 40 mol percent and higher. Accordingly, in commercial production of p-nitrophenetole steps are taken to minimize or suppress the runaway exothermic reactions that result in the formation of the azo and azoxy by-products. One effective way to control the formation of the azo and azoxy by-products is to introduce molecular oxygen in the liquid reaction mixture of p-nitrochlorobenzene, ethanol and aqueous sodium hydroxide. In order to optimize the control of the formation of the by-products, the oxygen content in the headspace above the reaction mixture is usually maintained above 15 mol percent. Oxygen being present in such high amount, together with ethanol, gives rise to a potential flammability and explosion hazard. As will be appreciated, a desired end would be to carry out the reaction at a lower oxygen content in the headspace while controlling the formation of azo and azoxy by-products. The present invention discloses a method that enables one to carry out the reaction of p-nitrochlorobenzene and ethanol with alkali metal hydroxide at significantly reduced levels of headspace oxygen while at the same time minimizing the formation of the azo and azoxy compounds.
U.S. Pat. No. 3,085,113 describes the ethoxylation of p-nitrochlorobenzene to produce p-nitrophenetole in the presence of air to suppress the occurrence of side reactions that result in the production of undesirable azo and azoxy compounds. In accordance with this known process, the air quantity must be carefully controlled in order to suppress the side reactions forming the azo and azoxy compounds.
Romanian Patent No. 62,677 discloses a process wherein the ethylation of p-nitrophenol with ethyl chloride is carried out in a polar aprotic solvent. In this known process, p-nitrophenol is used in the form of anhydrous sodium salts with the introduction of gaseous ethyl chloride as it is consumed in the reaction. N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone are mentioned in the patent as suitable polar aprotic solvents.
German Patent No. 2,639,700 describes the synthesis of p-nitrophenetole by reacting p-nitrochlorobenzene with ethanol in the presence of an alkali metal hydroxide in dimethyl sulfoxide solvent. This known method is not concerned with the use of an air sparge to minimize the formation of the azo and azoxy by-products.
U.S. Pat. No. 4,782,190 discloses preparing p-nitrophenetole by reaction of p-nitrochlorobenzene with ethanol and alkali metal hydroxides in the presence of a phase-transfer catalyst, such as the customary quaternary organic ammonium salts.